1. GENERAL
This specification defines minimum quality and technical
standards governing materials procurement, fabrication, testing and
installation of offshore pipelines installed by the S-lay (pipelay)
method. This specification is to be used
in conjunction with the following documents:
·
Basis of Design 84506-60-00-2L-060
·
General Specification
84506-60-00-2L-000 - Definitions and Specification Directory
·
General Specification
84506-60-00-2L-010 - Quality Assurance / Quality Control
·
General Specification
84506-60-00-2L-020 - General Offshore Specification
·
General Specification
84506-60-00-2L-040 - Offshore Survey
·
General Specification
84506-60-00-2L-050 - Offshore Positioning Systems
·
Project Specification
84506-60-00-2L-430 - Field Joint Coating Export Pipeline System
·
Project Specification
84506-60-00-2L-430 – Shrink Sleeve Field Joint Coating Infield System
·
DNV OS-F101 Submarine Pipeline Systems
2000
2. PIPELAY OPERATIONS
CONTRACTOR shall install pipelines in accordance with this
specification and DNV OS-F101 in order to prevent any damage and to maintain
the pipeline within acceptable stress limits.
Each installation procedure and piece of installation equipment shall be
developed and designed to control pipeline installation within the acceptable
stress limits.
2.1 For
each pipeline, CONTRACTOR shall submit to COMPANY for approval, detailed
documentation (procedures, drawings and associated pipelay analyses) describing
the equipment and the methods of control of stresses during pipelay. The documents shall include, as a minimum
those listed below, in addition to those required in referenced Project
Specifications.
·
S-Lay installation
·
Installation around pipeline radii
·
Pipelay initiation (subsea)
·
Pipeline abandonment and recovery
·
Pipelay termination
·
Static and dynamic pipelay analysis
·
Operating limit conditions
·
Anchoring/mooring procedures
·
Anchor patterns and catenaries
·
Field joint coating
·
Pipeline welding and NDT
·
Wet and dry buckle repair
·
Pipe tracking
·
Pipe coating repairs on the barge and
subsea
·
Material transportation, handling
storage and repair
·
Any other procedure(s) requested by
COMPANY
·
Touch down monitoring
2.2 Procedures
shall be supported by appropriate calculations and analysis showing compliance
with relevant Codes, Standards and Project Specifications, identifying the
calculation basis and any assumptions used.
CONTRACTOR shall furnish input and output data for calculations provided
in the form of computer output, and computer program descriptions to COMPANY
for approval.
2.3 Maximum
pipeline stress, along the entire route, during pipeline installation, burial,
repair, and pipe handling operations shall not under any conditions exceed the
limits listed in Table 2-1 with due consideration for the following:
·
Material manufacturing tolerances.
·
Potential variation in nominal
submerged weight.
·
Any other factor (e.g. field joint
stress intensification, vessel excursion), if that factor causes significant
changes in nominal pipe stress.
Table 2-1: ALLOWABLE
STRESS LIMITS
|
Operation
|
Maximum Allowable Stress
(% SMYS)*
|
|
|
Static
|
Dynamic
|
|
|
Pipe joint handling and transportation
|
72
|
72
|
|
Pipeline trenching and repair
|
72
|
72
|
|
Pipelay (including start-up/abandonment and recovery):
·
Sagbend region
·
Overbend region
|
72
85
|
96
96
|
* Specified Minimum Yield Strength
2.4 CONTRACTOR
shall provide, for COMPANY review and approval, details of all buckle detection
methods, including internal buckle detectors, diver / ROV inspection beyond the
touchdown point or constant tension monitoring and recording.
2.5 If
a buckle is suspected, CONTRACTOR shall carry out a detailed underwater video
inspection to check on the integrity of the installed pipelines. This inspection shall be carried out
immediately, unless directed otherwise by COMPANY.
Buckle detectors shall have a diameter 95% of the minimum
internal diameter of the pipe and shall be designed to ensure that no damage is
caused to the internal surfaces of the pipelines.
The buckle detector shall be pulled continuously through the
pipelines on a cable of sufficient length to ensure the pipelines are in the
final configuration on the seabed when the buckle detector passes. CONTRACTOR shall monitor and record the
performance of the detector at all times.
CONTRACTOR shall inform COMPANY of its intention to launch
or retrieve the buckle detector system.
COMPANY shall be notified in advance to allow witnessing of these
operations.
CONTRACTOR shall immediately notify COMPANY if the buckle
detector system fails or is suspected to have failed and when buckle detector
loads are higher than expected. In such
circumstances, CONTRACTOR shall remove the buckle detector for inspection.
2.6 During
pipelay start-up, laydown and crossings, pre-installed pipe supports and
through dredged areas, CONTRACTOR shall monitor pipe touchdown with an
ROV. Any adjustments in pipe position
required shall be immediately communicated to the laybarge.
3. TENSIONERS AND ROLLERS
CONTRACTOR shall determine the maximum, minimum and
set-point pipeline tension required for each 10 m water depth increment and/or
pipeline section submerged weight, plus the set-point barge configuration, as
part of its engineering analysis.
CONTRACTOR shall provide COMPANY with detailed schedules showing nominal
tensioner settings, pipe roller heights off deck, stinger roller heights and
vessel drafts. Analysis shall also
detail all operational limit conditions.
3.1 CONTRACTOR
shall determine the “deadband” allowing reasonable tension fluctuations, to
keep pipe stress within allowable limits under expected operating weather
conditions, and taking into account the specific dynamic motions of each
particular laybarge or lay vessel proposed.
3.2 CONTRACTOR
shall ensure tensioner squeeze pressure does not damage pipeline coatings or
anodes as they pass through each tensioner.
3.3 CONTRACTOR
shall limit maximum tension to the total fail-safe capacity of the least
capacity tensioner(s), i.e.; assuming the most powerful individual tensioner
has failed.
3.4 Tensioner
pads (track type) or rollers (wheel type) shall have molded polypropylene,
rubber or similar contact surfaces, and shall be fully intact. Any gouged, torn or worn tensioner pads or
rollers shall be replaced prior to starting pipelay, and CONTRACTOR shall provide
a reasonable amount of spare pads or wheels onboard the laybarge or at their
shore base.
3.5 CONTRACTOR
shall adjust all pipe rollers and stinger sections as required to provide
overbend and sagbend radii determined in the CONTRACTOR engineering
analyses. All rollers shall be fitted
with load cells. Each load cell shall be
monitored and loads recorded continuously during pipelay activities. All tension values from each tensioner and
combined tensions shall be monitored and recorded continuously during pipelay
activities.
3.6 Pipe
rollers shall have molded polypropylene, rubber or similar contact surfaces,
and shall be fully intact. Any gouged,
torn or worn pipe rollers shall be replaced prior to starting pipelay.
3.7 Abandonment
and recovery (A&R) winch shall be monitored and cable tension recorded
continuously during operation.
4. PIPELINE INITIATION / LAYDOWN HEADS
4.1 CONTRACTOR
shall design pipeline heads and deadman anchors to withstand design initiation
and laydown forces.
4.2 Pipeline
initiation and laydown heads that are to be used for pipeline hydrotests and
dewatering shall be designed for the maximum hydrotest pressure, and shall be
subject to a leak test prior to use.
Those heads designed for pig launching and /or receiving shall have
valve, manifold and pig stop arrangements designed for independent operation of
individual pigs and shall be pressure tested to the ratings of the valves prior
to use. All check valves shall be spring
loaded to ensure the pipeline is not inadvertently flooded.
4.3 Protection
frame(s) designed to prevent accidental valve operation on contact with stinger
rollers or the seabed shall enclose valves incorporated into an initiation or a
laydown head.
4.4 Skids
designed to smooth the transition of pipe flanges over the stinger rollers
shall enclose flanges and be removed when the pipe is on the seabed.
Valve
handles or wheels shall be readily accessible by a diver or ROV, as
appropriate, and each valve shall be clearly designated in high visibility
paint with a unique number, letter or combination thereof.
5. LINEPIPE AND MATERIALS HANDLING AND REPAIR
Linepipe shall be handled in accordance with Project
Specification for Handling, Storage and Transportation of Linepipe
84506-60-30-2L-270. Other materials shall be handled according to accepted
industry practice. Damage detected
before the pipe enters the water shall be repaired immediately.
5.1 Anode
pipe joints shall be stored to allow installation in the proper sequence. CONTRACTOR shall take special care to ensure
the electrical bond from anode bracelet to pipe is not damaged during handling,
storing and installation of these pipe joints.
5.2 CONTRACTOR
shall test any suspect anode for electrical continuity with the pipe, prior to
welding the anode pipe joint into the line.
5.3 CONTRACTOR shall provide an appropriate
quantity of spare permanent materials as necessary to meet potential repair
scenarios. Proposed contingency
materials and quantities shall be subject to COMPANY approval.
5.4 CONTRACTOR shall immediately notify
COMPANY when any pipeline damage has occurred.
CONTRACTOR shall repair or replace any damaged steel, weld, anode, field
joint coating or yard applied coating which affects pipeline useful life or
mechanical integrity. COMPANY shall make
the final decision as to whether pipe damage has occurred, or to what extent
damage has occurred. All repair material and procedures shall conform to the
Project Specifications.
5.5 Pipe joints which are dented, gouged,
out-of-round, or have wall thickness reduction greater than allowed by the
Project Specification for Linepipe 84506-60-30-2L-210 shall be replaced. COMPANY shall make the final decision as to
the amount of damage that can be repaired, and the amount of material that
shall be replaced.
5.6
No weld repairs
shall be made on dents, grooves, deep scratches, gouges, major arc burns, or
other defects which may affect parent metal integrity. Pounding out or jacking out dents in
out-of-round pipe joints is prohibited.
Minor arc burns, scratches or other minor pipe joint parent metal
surface defects may be repaired by grinding, subject to COMPANY approval,
provided that minimum allowable pipe wall thickness is maintained.
6. PIPELAY INSTALLATION
Installation shall be in accordance with COMPANY approved
procedures. COMPANY approval of any
procedure does not relieve CONTRACTOR of the full responsibility to provide a
properly constructed pipeline to COMPANY satisfaction.
6.1 CONTRACTOR
shall perform a pre-lay survey in accordance with Project Specification for
Offshore Survey 84506-60-00-2L-030 to ensure the pipeline route is clear of
obstructions. CONTRACTOR shall clear all
debris, natural or otherwise, which would interfere with submarine pipeline installation,
prior to offshore installation.
6.2 CONTRACTOR
shall position pipeline installation vessel(s), survey vessels and
anchor-handling tugs, in accordance with Project Specification for Offshore
Positioning Systems 84506-60-00-2L-050. Installation vessel positioning data,
anchor placement logs and as-built survey data shall be made available to
COMPANY and installation vessel personnel at all times during
installation. Copies of raw data shall
also be made available to COMPANY.
6.3 CONTRACTOR
shall inspect and survey the installed facilities through all stages of
construction using divers or ROVs in accordance with Project Specifications for
Offshore Survey 84506-60-30 -2L-030 and As-Built Survey 84506-60-00-2L-040.
6.4 CONTRACTOR
shall install the pipeline along the route shown on the Project Approved Drawings.
Along pre-trenched or dredged sections of the pipeline route, CONTRACTOR
shall install the pipeline in the bottom of the trench. The pipeline shall be laid on-bottom within
the following tolerances from the pipeline centerline coordinates:
·
+/- 6.0 m along the pipeline corridor.
·
+/- 3.0 m within 500 m of a subsea
flange tie-in (PLEM, manifold, riser).
·
+/- 2.5 m within 10 m of any
pre-trenched/support areas.
6.5 The
pipeline termination flange, and any dummy spool, shall be positioned on the
seabed to within +/- 2.5 meters of the target co-ordinate and the pipeline
heading shall be +/- 1°.
6.6 Each
pipe joint shall be internally cleaned and gauged to remove dirt, loose rust
and to ensure acceptable pipe joint ovality by a COMPANY approved method,
immediately prior to welding. Gauging
plates shall be sized to comply with Project Specification for Cleaning,
Gauging and Hydrotesting 84506-60-30-2L-390.
Pipes failing the pre-installation gauging test shall be clearly marked
as rejected and stored in a dedicated location for rejected pipe until such
rejected pipe can be removed from SITE.
6.7 CONTRACTOR
shall string pipe joints in the required sequence of materials, wall thickness,
coating type and anode joints, as shown on the Project Drawings.
6.8 Prior
to welding operations, all weld bevels shall be cleaned by COMPANY approved
methods. CONTRACTOR shall cut and
rebevel defective or damaged bevels.
6.9 CONTRACTOR
shall mark each pipe joint with a sequential number, when welded to the pipeline. The numbers shall be painted clearly on both
sides of the pipeline coating adjacent to the field joint at one end of the
pipe joint, using white paint suitable for immersion in seawater. The digits shall be large enough to be easily
read on an ROV video monitor.
6.10 CONTRACTOR
shall not move the pipe-string down the pipelay ramp, until both root bead and
hot pass have been completed at the first welding station, unless it can be
fully demonstrated to COMPANY’s complete satisfaction by analysis that pulling
on the root bead will not cause any detrimental effects taking into account all
barge operational characteristics and conditions.
6.11 CONTRACTOR shall maintain a continuous
record of each pipe joint incorporated into the pipeline, and shall submit this
record (Pipe and Weld Record) daily to COMPANY, with the following information:
·
Pipe joint identification number
·
Pipe joint heat number
·
Pipe joint length
·
Anode joint or standard
·
Cumulative length
·
Weld number
·
Time and date the pipe joint is stalked
on and welded
·
NDT results
·
Weld repairs
·
Weld cut outs with amended pipe joint
length records
·
Concrete weight-coating thickness
·
Tension Recorded.
The Pipe and Weld Record shall be
entered onto the CONTRACTOR’s tally/QC system as a minimum at the end of every
shift. Pipe and Weld Record format and
documentation procedures shall be approved by COMPANY prior to mobilization.
An electronic copy of data listed above
will be made available to the COMPANY.
7. PIPELAY ABANDONMENT AND RECOVERY
CONTRACTOR shall submit abandonment and
recovery procedures, for COMPANY approval.
CONTRACTOR shall identify circumstances for complete pipeline
abandonment and circumstances for partial pipeline abandonment (to avoid high
pipelay stresses but at the same time keep the abandonment and recovery cable
connected to the pipeline) including:
·
Weather or sea conditions preventing
safe pipeline installation.
·
Malfunction of major equipment
preventing safe pipeline installation.
·
Dry and wet buckles.
7.1 CONTRACTOR shall abandon pipelines only
if absolutely necessary to prevent damage to the pipeline, coatings or marine
equipment and / or where personnel safety is a concern. COMPANY shall be notified prior to starting
any abandonment or recovery operations.
For
abandonment and recovery, CONTRACTOR shall weld a temporary A&R head to the
pipeline, and make all other preparations to lower the pipeline to the
seabed. CONTRACTOR may elect to
partially abandon or completely abandon the pipeline at his discretion.
7.2 In the event that the abandonment /
recovery cable is released from the installation vessel. CONTRACTOR shall mark
the pipeline head with a buoy and a survey fix.
7.3 When pipelay is able to re-commence,
pipeline recovery operations shall begin in accordance with COMPANY approved
procedures.
7.4 Abandonment or recovery operations shall
not cause pipe stress to exceed allowable stress limits.
8. WELDING
CONTRACTOR shall perform pipeline welding in accordance with
Project Specification for Pipeline Welding 84506-60-30-2L-330.
9. NON-DESTRUCTIVE TESTING
CONTRACTOR shall perform pipeline
welding radiography and other non-destructive examination (NDT) in accordance
with Project Specification for Pipeline Weld NDT (84506-60-30-2L-340).
10. FIELD JOINT COMPLETION
CONTRACTOR shall complete pipeline field joints in
accordance with relevant Project Specifications for Field Joints
84506-60-30-2L-430 .
11. PIPELAY SURVEY
CONTRACTOR shall perform pipelay survey operations in
accordance with Project Specification for Offshore Survey 84506-60-30-2L-030
and As Built Survey 84506-60-30-2L-040.
12. ANCHOR HANDLING
CONTRACTOR shall perform anchor handling in accordance with
Project Specification for General Offshore Specification 84506-60-30-2L-020.